A well-known inspection apparatus for filter cigarettes analyzes the color components of an inspection image obtained by photographing the end face of a filter and determines the presence or absence of dust or dirt adhered to the filter end face (see Patent Document 1, for example).
It has also been proposed, instead of adding a flavor component to tobacco leaves, to embed a string-like flavor containing element 3 in a columnar filter 2 attached to one end of a cigarette 1 as shown in FIG. 4 (see Patent Document 2, for example). The flavor containing element 3 of this type includes a string (thread) made of fiber which is called an aroma-chemical preserving composite fiber and having a diameter of about 1 mm, and a flavor component, such as peppermint and menthol, contained in the string. The string-like flavor containing element 3 is embedded, for example, along the axis of the filter 2.